Influence on the luminescence europium complex by localized surface plasmon of silver and gold nanoparticles

Many studies on luminescence enhancement by surface plasmons were reported, among which metal nanoparticles were paid many attentions to, because of their special optical properties. The localized surface plasmon resonance can be tuned by changing nanoparticles' size, shape, interparticle spacing, and dielectric environment. They can be used for altering the optical properties of luminescence materials, and are used in the rare earth (RE) ions doped materials. For the RE doped materials, according to the Fermi golden rule, the spontaneous emission rate from excited level |i> to lower level |j> is Γ_ij∝|M_ij|²ρ(ν_ij), where M_ij is the matrix element related to the two energy levels, ρ_ij is the optical density and is also known as the photon mode density (PMD). In the present work, we experimentally demonstrated the influence of silver and gold metal nanoparticles on the luminescence of Eu complex. These nanoparticles had different sizes and shapes, including the silver spheres, nanoprisms and nanocubes, and gold nanoprisms. Based on the luminescence, lifetime and nanoparticles' absorption measurement, the different luminescence enhancement was obtained. The enhancement of luminescence had a great relationship with the overlap between the nanoparticles' localized surface plasmon resonance bands and the emission or excitation wavelengths. Their influence on the lifetime were also different, which meant the different infuence on the radiative and non-radiative decay rate. We further confirmed that the different influence of these nanoparticles partly came from the variation in the photon mode density (PMD).